Transmitter apparatus and radio communication method

ABSTRACT

A radio station equipped with an array antenna, when transmitting an information symbol sequence to a particular radio station, uses a plurality of vectors, which are produced based on a propagation channel characteristic established between these radio stations, to simultaneously transmit a plurality of symbol sequences, which include the information symbol sequence, by way of vector multiplexing, thereby causing the particular radio station to receive the information symbol sequence, while causing other radio stations of different propagation channels to simultaneously receive a part or all the plurality of symbol sequences. Thus, when data is transmitted to a particular radio station via a radio communication channel, the concealment of information can be secured with a high level of security.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION PCT/JP2004/001449.

TECHNICAL FIELD

The present invention relates to a transmitter apparatus and radiocommunication method for transmitting the information requiringconcealment at between particular radio stations by way of a radiocommunication channel.

BACKGROUND ART

Recently, digital radio communication has occupied the importantposition in the telecommunication field by virtue of its drasticimprovement in transmission speed and quality. Meanwhile, radiocommunication, making use of a radio wave space as a public property,involves a fundamental drawback that interception might be by a thirdparty when considered from a concealment point of view. Namely, therealways exists a fear that the communication content be intercepted byand leaked of information to the third party.

Accordingly, the conventional radio communication is devised byencrypting information in such a manner that, should communication databe intercepted by a third party, information content could not be knownto the third party. Encryption is now under study and applied in variousfields. This is owing to the benefit of encryption that a constant levelof security is to be secured without modifying the communication system.

However, information encryption involves a problem that information iscomparatively easy to crack where the encryption code or its procedurebecomes aware of. Particularly, in the existing situation thathigh-speed computers are generally in widespread dissemination, securityis not to be secured without the use of a significantly complicatedencryption process.

To cope with the problem encountered in such an encryption art, there isproposed a radio transmission scheme with high level of concealmentbased upon the notice to the physical feature of a propagation channel,that is, radio wave propagation medium (e.g. JP-A-2002-152191).According to this method, communication data is exchanged by taking intoaccount the propagation channel characteristic shared between theparticular radio stations. Because of the impossibility to receive orrestore the data at other radio stations having different propagationchannels, security can be obtained on the physical layer of radiocommunication. Meanwhile there is another art that a secret key isshared between particular radio stations in order to encrypt data basedupon a propagation channel having a characteristic unique to those,thereby preventing the third party from eavesdropping (e.g. MotokiHoriike and three others, “A Scheme of Secret Key Agreement Based on theRandom Fluctuation of Channel Characteristics in Land Mobile Radio”,Shingaku-giho, RCS2002-173, October 2002).

In those radio transmission schemes making use of the randomness overthe radio transmission channel, the communication data requiringconcealment can be prevented from being intercepted by raising theprobability of error occurrences over the transmission channel upon aninterception by a third party. Accordingly, communication is madepossible with higher security by combining it with an information sourcekey encryption technique in general utilization.

In the mobile communication system of cellular telephony or WLAN, thepropagation channel characteristic between two radio stations, usually,is characterized by the spatial locations of radio stations. Theparameters describing the propagation channel characteristic usesamplitude/phase, arrival wave directions, delay time, polarization andso on. In case the propagation channel between particular radio stationscan be uniquely characterized by use of those parameters, communicationcould be realized with concealment by taking propagation parameters intoconsideration. The uniqueness can be considered enhanced furthermore byincreasing the number of parameters and expressing the propagationchannel characteristic by means of a multi-dimensional parameter.

However, where implementing radio communication while taking intoconsideration the propagation parameters estimated from the propagationchannel between the radio stations, in case attempted to increase thenumber of parameters or improve the estimation accuracy of parametersfor improving concealment, there arises a problem that higher accuracyis required for the hardware besides the increased amount of signalprocessing.

Meanwhile, in the case of producing a common key for use in encryptiondepending upon the propagation parameters, both the two radio stationsare required to execute the process of propagation parameter estimationand key production. For example, assuming the communication between thebase station and the terminal, there is a problematic need to improvethe hardware accuracy of the communication terminal on a tendency towardupgraded functions, particularly, as to applications and interfaces, inorder to increase signal processing amount and ensure estimationaccuracy.

DISCLOSURE OF THE INVENTION

The present invention is for solving the problem in the prior art, andit is an object thereof to provide a transmitter apparatus and radiocommunication method capable of preventing the data requiringconcealment from leaking to a third party over the communication channelwithout the need for an encryption process, etc. using a propagationparameter after estimating the propagation parameter featuring apropagation channel of between particular radio stations forcommunication.

In the radio communication method of the invention, a radio stationhaving an array antenna, upon transmitting data wirelessly to aparticular radio station that communication is desired, is allowed totransmit, with vector multiplexing, a plurality of ones of datasimultaneously besides to-be-notified data by use of a vector spacefeaturing a propagation channel of between the radio stations. At theparticular radio station as the opposite of communication, only adesired to-be-notified data sequence is to be received while securing aconstant channel quality owing to an array antenna gain. Furthermore, atanother radio station as a third party, a plurality of ones of data areto be simultaneously received in addition to the to-be-notified data.Due to this, other radio station as a third party is to receive a signalcontaining a plurality of ones of data as interference signalcomponents, i.e. deteriorated in SINR (Signal to Interference and NoiseRatio). This raises the probability of error occurrences in thedemodulated signal sequences, making it difficult to extract andcorrectly restore the particular data transmitted between particularradio stations.

In this manner, the data sequence requiring concealment can be preventedfrom leaking to a third party over the transmission channel of radiocommunication without the need of encryption processing, etc. using thepropagation parameter after estimating the propagation parameterfeaturing a propagation channel of between the particular communicatingradio stations.

A transmitter apparatus of the invention is a transmitter apparatus fortransmitting an information symbol sequence from a first radio stationhaving an array antenna having M (M>1) elements to a second radiostation, the transmitter apparatus comprising: vector control means forproducing a plurality of N (N<=M) dimensional vectors depending upon apropagation parameter featuring a propagation channel of between thefirst radio station and the second radio station; and vectormultiplexing means for producing vector-multiplexed symbol sequences inthe number of N multiplexed by multiplying the plurality of Ndimensional vectors on a plurality of symbol sequences containing theinformation symbol sequence; whereby the vector control means transmits,at the array antenna, the vector-multiplexed symbol sequences set suchthat, at the second radio station, a particular symbol sequence only isto be received of among a plurality of the symbol sequences whereasother symbol sequences are to be canceled.

Due to this, where there exist the first radio station for transmittingthe information symbol sequence and another radio station being not thesecond radio station, the other radio station is to receive part or allof the plurality of symbols. Hence, the other radio station is madedifficult to restore the information symbol sequence. Thus, informationleakage is prevented and communication security is ensured.

Meanwhile, a transmitter apparatus according to the invention furthercomprises propagation channel analyzing means for producing apropagation channel matrix as the propagation parameter, the vectorcontrol means being to produce a plurality of N dimensional vectorsobtained by singular-value decomposition of the propagation channelmatrix.

Due to this, because the second radio station is allowed to receive theinformation symbol sequence without undergoing interference from othersymbol sequences, communication quality of the radio channel can beimproved.

Meanwhile, a transmitter apparatus according to the invention furthercomprises propagation channel analyzing means for producing apropagation channel matrix as the propagation parameter, the vectorcontrol means being to produce a plurality of N dimensional vectorsobtained by eigen-value decomposition of the correlation matrix of thepropagation channel matrix.

Due to this, because the gain of the M-element array antenna held by thefirst radio station can be maximized on the propagation channel, linkbudget of the radio channel can be improved.

Meanwhile, a transmitter apparatus according to the invention furthercomprises reference symbol producing means for producing a referencesymbol known also to the communicating terminal and propagation channelinformation receiving means for receiving information about propagationparameter transmitted from the communicating terminal and determiningthe propagation parameter, the information about propagation parameterbeing produced from a propagation parameter the communicating terminaldetermined from the reference symbol transmitted from the base station.

Due to this, because it is possible to correctly obtain the informationabout a propagation channel for the communicating-terminal antenna asviewed from the base station array antenna, the performance can bemaintained even under such a condition that the asymmetry of downlinkand uplink is not negligible.

Meanwhile, a transmitter apparatus according to the invention is atransmitter apparatus wherein the plurality of symbol sequences, in partor all, are symbol-mapped based on modulation schemes different one fromanother.

Due to this, the other radio station than the first and second radiostations is to receive part or all of the other symbol sequencedifferently modulated from the information symbol sequence, the signalcorrelation between the information symbol sequence and the other symbolsequence can be decreased to reduce the probability of demodulation ofthe information symbol sequence at the other radio station.

Meanwhile, a transmitter apparatus according to the invention is atransmitter apparatus wherein the plurality of symbol sequences, in partor all, are spread by code sequences different one from another.

Due to this, because of the structure easy to vary the code sequence,even where there should be such a propagation situation that thepropagation channel has a high correlation characteristic to thepropagation channel of between the first radio station and the otherradio station, the code sequence for use in the information symbolsequence, if properly varied, enables control not to demodulate theinformation symbol sequence at the other radio station.

A radio communication method according to the invention comprises: astep of transmitting, from a communicating terminal to a base stationhaving an array antenna having M elements, a reference signal made up byreference symbols known to the base station; a step for the base stationto calculate a propagation parameter of between the communicatingterminal and the base station from the received reference symbols in thenumber of M and produce a plurality of N dimensional vectors by usingsame; a step for the base station to multiply a plurality of symbolsequences containing a to-be-notified information symbol sequence, bythe plurality of N dimensional vectors set such that at thecommunicating terminal the to-be-notified information symbol sequenceonly is to be received while other information symbol sequences are tobe canceled, and to produce vector-multiplexed symbol sequencesmultiplexed and in the number of N; and a step of transmitting thevector-multiplexed symbol sequences from the base station to thecommunicating terminal.

Due to this, in a mobile communication system represented by cellulartelephony or WLAN, the location, surrounding environment, etc. of thecommunicating terminal follows the change in time of propagation channelcharacteristic as caused by time change. Accordingly, the base stationanalyzes the propagation parameter featuring the propagation channel byuse of the reference signal sent from the communicating terminal, andtransmits a particular symbol sequence by use of the vector-multiplexedsymbol sequence obtained by a vector-multiplexed process based on theanalysis result of same. Accordingly, in the mobile communication systemchanging in propagation channel characteristic, the other radio stationis difficult to restore the information symbol sequence. Thus,information leakage is prevented and communication security is ensured.

Meanwhile, a radio communication method of the invention comprises: astep of transmitting, from a base station having an array antenna havingM elements to a communicating terminal, a reference signal made up byreference symbols known to the communication terminal; a step for thecommunicating terminal to produce a propagation channel informationsymbol sequence containing a propagation parameter of between thecommunicating terminal and the base station, from the received referencesignal; a step of transmitting the propagation channel informationsymbol sequence from the communicating terminal to the communicationterminal; a step for the base station to calculate the propagationparameter from the received propagation channel information symbolsequence and producing a plurality of N dimensional vectors by using ananalysis result of same; a step for the base station to multiply aplurality of symbol sequences containing a to-be-notified informationsymbol sequence, by the plurality of N dimensional vectors set such thatat the communicating terminal the to-be-notified information symbolsequence only is to be received while other information symbol sequencesare to be canceled, and to produce vector-multiplexed symbol sequencesmultiplexed and in the number of N; and a step of transmitting thevector-multiplexed symbol sequences from the base station to thecommunicating terminal.

Due to this, the second radio station is allowed to feed the analysisresult on the propagation parameter featuring the propagation channelback to the first radio station. Accordingly, where the propagationchannel is asymmetric as to transmitting and receiving, e.g. in a radiocommunication system using frequencies different upon betweentransmitting and receiving, communication is possible with high securityensured.

According to the radio communication method of the invention so fardescribed, a desired data sequence only is to be exchanged whilesecuring a constant level of channel quality between particular radiostations. At the other radio station, or third party, a plurality ofdata sequences are to be simultaneously received with superimposition inaddition to the desired data sequence. This can prevent the datasequence requiring concealment from being received by a third party onthe communication channel, thus securing the high level of security overthe radio communication channel.

Meanwhile, it is possible to transmit and receive a transmission datasequence, of from another radio station, to possibly cause interferenceover the radio channel established between particular radio stations,separately from the desired data sequence. Thus, interference tolerancecan be improved for a radio communication system allowing a plurality ofusers to have accesses.

Meanwhile, in the invention, after estimating a multi-dimensionalpropagation parameter featuring the propagation channel of between theparticular radio stations communicating, there is no need to carry out aprocessing of encryption, etc. using the propagation parameter. Thus,there is no need of signal processing amount increase or hardware highaccuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an arrangement of a radiocommunication system according to embodiment 1 of the present invention.

FIG. 2 is a concept diagram showing a feature of the radio communicationsystem according to embodiment 1 of the invention.

FIG. 3 is a block diagram showing a configuration of a base stationaccording to embodiment 1 of the invention.

FIG. 4 is a block diagram showing the configuration of a communicatingterminal according to embodiment 1 of the invention.

FIG. 5 is a figure showing a transmission frame structure of a referencesymbol according to embodiment 1 of the invention.

FIG. 6 is a block diagram showing a configuration of multi-symbolproducing means according to embodiment 1 of the invention.

FIG. 7 is a figure showing a frame structure of communication accordingto embodiment 1 of the invention.

FIG. 8 is a figure showing a frame structure of communication accordingto embodiment 1 of the invention.

FIGS. 9A to 9C are figures showing a received signal waveform accordingto embodiment 1 of the invention.

FIG. 10 is a figure showing a leak ratio of communication data accordingto embodiment 1 of the invention.

FIG. 11 is a figure showing a procedure of communication according toembodiment 1 of the invention.

FIG. 12 is a block diagram showing a configuration of a base stationaccording to embodiment 2 of the invention.

FIG. 13 is a block diagram showing a configuration of a communicatingterminal according to embodiment 2 of the invention.

FIG. 14 is a figure showing a frame structure of communication accordingto embodiment 2 of the invention.

FIG. 15 is a figure showing a frame structure of communication accordingto embodiment 2 of the invention.

FIG. 16 is a figure showing a frame structure of communication accordingto embodiment 2 of the invention.

FIG. 17 is a figure showing a procedure of communication according toembodiment 2 of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, embodiments of the present inventionwill now be explained in detail in the below.

(Embodiment 1)

FIG. 1 is a block diagram showing an overall arrangement of a radiocommunication system 100 of the invention. In the figure, the radiocommunication system 100 is configured with a base station 101, acommunicating terminal 102, and a propagation channel 103 of between thebase station 101 and the communicating terminal 102. The base station101 has a base station transmitter-receiver section 104 and a basestation array antenna 105 while the communicating terminal 102 has aterminal antenna 106 and a terminal transmitter-receiver section 107.The data sequences D1–DK in the number of K, to be transmitted from thebase station 101, are sent in the form of vectorized signals x1–xK as tothe data sequences D1–DK through the base station array antenna 105 tothe communicating terminal 102.

FIG. 2 shows a system operation principle for realizing to ensure thesecurity of transmission data on the radio communication system 100. InFIG. 2, the base station 101 is to transmit the vectorized signals x1–xKthrough the propagation channel 103 to the communicating terminal 102whereas, to the non-communicating terminal 200, desirably the data fromthe base station 101 is prevented from leaking. This is in a locationspatially different from the communicating terminal 102 with respect tothe base station. Meanwhile, the propagation channel 201 is shown as apropagation channel lying between the base station 101 and thenon-communicating terminal 200. In urban areas with densely packedbuildings or in wall-surrounded indoor environment of radio wavepropagation, the propagation channels to a plurality of communicatingterminals, spatially different in location with respect to the basestation, exhibit characteristics different one from another due tomulti-path propagation. Particularly, it is known that the complexenvelope fluctuations of received signals, taking place with movement ofcommunicating terminals or with passage of time, have a probabilitydistribution that can be modeled according to Rayleigh distribution.Between the different communicating terminals, there is no correlationas to the fluctuation characteristics of received signals.

In the radio communication system 100 of this embodiment, the basestation 101 transmits, with vector multiplexing, the data sequencesD1-DK simultaneously through the base station array antenna 105, inaccordance with the propagation channel 103. It is now assumed that thetransmit vector-multiplexed signal is transmitted to the communicatingterminal 102 by way of the propagation channel 103. When control is donefor the communicating terminal 102 to receive a vectrorized signal x1 ofthe data sequence D1 at high sensitivity, the non-communicating terminal200 is caused to receive part or all of the vector signals x2–xK of thedata sequences D2–DK simultaneously besides the vectorized signal x1 ofthe data sequence D1. This is because the propagation channel 201exhibits a characteristic less correlated to the propagation channel103. Due to the previous control for the communicating terminal 102 tohave a higher correlation as to x1 to the propagation channel 103 whilehaving a lower correlation of vectorized signals x2–xK to thepropagation channel 103, control is effected to provide statistically ahigher correlation of the vectorized signals x2–xK than the vectorizedsignal x1 to the propagation channel 201. Accordingly, when the basestation is to convey the information of data sequence D1 to thecommunicating terminal 102, in case information is previously providedto the data sequences D2–DK differently from the data sequence D1, thenon-communicating terminal 200 is made difficult to receive only thedata sequence D1 and restore the information thereof.

With reference to FIGS. 3 to 11, explanation is made in detail below onthe radio communication system 100 that the base station 101 is totransmit a plurality of data sequences by vector multiplexing to therebyprevent the information leak to the non-communicating terminal 200 andhence ensure the security of communication between the base station 101and the communicating terminal 102 over the radio channel.

FIG. 3 shows a configuration of the base station transmitter-receiversection 104 and base station array antenna 105 in the base station 101.In the figure, the base station transmitter-receiver section 104 isconfigured with multi-symbol producing means 300, vector multiplexingmeans 301, base station RF section 302, propagation channel analyzingmeans 303, transmit-vector control means 304 and array-combinedreceiving means 305. Meanwhile, the base station array antenna 105 isstructured with antenna elements A1–AM in the number of M.

FIG. 4 shows a configuration of the terminal transmitter-receiversection 107 in the communicating terminal 102, 200. In FIG. 4, theterminal transmitter-receiver section 107 is configured withreference-symbol producing means 400, symbol producing means 401, aterminal RF section 402 and decode means 403.

In this embodiment, the communicating terminal 102 transmits a referencesignal x0 at the terminal antenna 106. The reference signal x0 is to bereceived by the base station 101 in order to analyze the propagationchannel 103. This contains a reference signal previously shared betweenthe base station 101 and the communicating terminal 102.

In the outset, the transmit operation at the communicating terminal 102is explained below by use of FIG. 4.

In FIG. 4, the reference-symbol producing means 400 produces aparticular reference symbol R0 previously agreed between the basestation 101 and the communicating terminal 102, and forwards it to thesymbol producing section 401. The symbol producing means 401 makes up atransmission frame 500 by the received reference symbol R0 and, ifrequired, by a pilot symbol P0, address symbol A0 and frame check symbolFC0 added to the data sequence D0 symbol-mapped in accordance withmodulation scheme, thereby outputting it as a symbol sequence S0 to theterminal RF section 402. The terminal RF section 402 converts the symbolsequence S0 into a radio band signal and transmits it as a referencesignal x0 to the base station 101 through the terminal antenna 106.

In FIG. 5, note that, for receiving , the reference symbol R0 is used asa reference symbol, the pilot symbol P0 as frame synchronizationestablishment, the address symbol A0 as terminal authentication and theframe check symbol FC0 for use in bit-error detection upon of receiving.Meanwhile, the symbol-mapped data sequence D0 is inserted, as required,upon transmission. However, where the symbol sequence is used for themere purpose of analyzing the propagation channel 103, it may bestructured to transmit the reference symbol R0 only. Meanwhile, wherethe base station 101 is to estimate an arrival wave direction orpolarization from the received signals at the antenna elements A1–AM ofthe base station array antenna 105 and to calculate for the propagationchannel 103 depending upon the result thereof, there is not always aneed to transmit a reference symbol R0 from the communicating terminal102.

Now, the receive operation at the base station 101 is explained below byuse of FIG. 3.

In FIG. 3, the reference signal x0, sent from the terminal antenna 106,is received by the base station array antenna 105 by way of thepropagation channel 103. The received signals at the antenna elementsA1–AM of the base station array antenna 105, are respectively convertedinto received symbol sequences Y1–YM as baseband signals in the basestation RF section 302, and outputted to the propagation channelanalyzing means 303. The propagation channel analyzing means 303 takesas an input the received symbol sequences Y1–YM, to produce apropagation channel matrix H as a propagation parameter featuring thepropagation channel 103. The elements constituting the propagationchannel matrix H are complex channel coefficients h1–hM calculated fromthe amplitude and phase of a reference symbol R0 component contained inthe received symbol sequences Y1–YM. Hence, the propagation channelmatrix H is to be expressed as in (Equation 1).H=[h1 h2 . . . hM]  (1)

Incidentally, how to calculate a propagation channel matrix H here wasexplained with the method using a reference symbol R0, or known signal.Alternatively, it is possible to estimate any or all of the frequency,delay time, incident direction and polarization of an arrival wavedepending upon the received signals at the antenna elements A1–AM of thebase station array antenna 105, and to estimate a propagation channelmatrix H depending upon the result thereof.

Then, the vector control means 304 makes a singular-value or eigen-valuedecomposition of the propagation channel matrix H by use of thepropagation channel matrix H as an input, and produces a transmittingvector space V and a receiving vector space V′. It is assumed here thatthe vector space V determined from H is formed by a matrix spacecomprising column vectors having K (K<=M) rows and in the number of M (Mdimensions) as shown in (Equation 2) while the vector space V′ is amatrix space comprising column vectors having L (L<=M) rows and in thenumber of M (M dimensions) as shown in (Equation 3).

$\begin{matrix}{\begin{bmatrix}V_{1} \\V_{2} \\\vdots \\V_{K}\end{bmatrix} = \begin{bmatrix}V_{11} & V_{21} & \ldots & V_{M1} \\V_{12} & V_{22} & \ldots & V_{M2} \\\vdots & \vdots & \ldots & \vdots \\V_{1K} & V_{2K} & \ldots & V_{MK}\end{bmatrix}^{T}} & (2) \\{\begin{bmatrix}V_{1}^{\prime} \\V_{2}^{\prime} \\\vdots \\V_{L}^{\prime}\end{bmatrix} = \begin{bmatrix}V_{11}^{\prime} & V_{21}^{\prime} & \ldots & V_{M1}^{\prime} \\V_{12}^{\prime} & V_{22}^{\prime} & \ldots & V_{M2}^{\prime} \\\vdots & \vdots & \ldots & \vdots \\V_{1L}^{\prime} & V_{2L}^{\prime} & \ldots & V_{ML}^{\prime}\end{bmatrix}^{T}} & (3)\end{matrix}$Note that T represents a transposition action to the matrix.

Now explanation is made on the procedure for calculating a vector spaceV. First explained is a calculation procedure based on singular-valuedecomposition.

(Equation 4) shows singular-value decomposition of a propagation channelmatrix H shown in (Equation 1).H=U·Δ·Vs ^(H)  (4)

Note that, concerning the right side of (Equation 4), Δ is a matrix withone row and M columns, having a singular value of H as a matrix element.Meanwhile, Vs is a vector space constituted by mutually orthogonalcolumn vectors vs1–vsM having M rows (M dimensions) and in the number ofM. Those can be expressed as (Equation 5) to (7), respectively.

Meanwhile, Vs^(H) shows a matrix assuming a complex conjugatetransposition to the matrix Vs. Furthermore, because H is a matrix withone row and M columns, singular value is to be sought only one in thenumber, which here is assumed as δ.U=1  (5)Δ=[δ 0 . . . 0]^(T)  (6)Vs=[vs1 vs2 . . . vsM]  (7)

Now explained is a case of using eigen-value decomposition. The vectorcontrol means 304 calculates first a correlation matrix R on thepropagation channel matrix H of (Equation 1) by using (Equation 8).R=H*·H  (8)

Note that * represents the action of a complex conjugate transpositionto the matrix. As shown in (Equation 9), the correlation matrix R isdecomposed by eigen values and eigen vectors to calculate a squarematrix λ with M rows and M columns having a diagonal term of eigenvalues, and a vector space Ve.R·Ve=λ·Ve  (9)Here, Ve is a vector space constituted by mutually orthogonal columnvectors ve1–veM with M rows (M dimension) and in the number of M,wherein k is a matrix with M rows and M columns having a diagonal termof squared values of the elements of the foregoing Δ and the otherelement all assuming 0.

Furthermore, the vector control means 304 selects column vectors in thenumber of K out of the column vectors in the number of M constituting Vsobtained by singular-value decomposition or Ve obtained by eigen-valuedecomposition, and outputs those as a transmitting vector space V. Also,it selects column vectors in the number L and outputs those as areceiving vector space V′.

Next, explanation is made on the transmit operation of data sequencesD1–DK at the base station 101.

As shown in FIG. 6, the multi-symbol producing means 300 of the basestation transmitter-receiver section 104 is configured with encode means600-1–600-K in the number of K and frame producing means 601-1–601-K. Atfirst, the encode means 600-1–600-K uses the data sequences D1–DK as aninput and executes a symbol-mapping process over a complex plane inaccordance with modulation scheme. Furthermore, the frame producingmeans 601-1–601-K adds the symbol-mapped data sequences D1–DK with pilotsymbols P1–PK for frame synchronization, address symbols A1–AK forinformation source identification and frame. check symbols FC1–FCK forbit error detection upon reception, to thereby produce transmissionframes 700-1–700-K and output those to the vector multiplexing means.

The vector multiplexing means 301 uses, as an input, the symbolsequences S1–SK comprising the transmission frames 700-1–700-K andexecutes a vector multiplexing process as shown in (Equation 10) by useof the vector space V constituted by the vectors v1–vK produced by thevector control means 304, thus producing vector-multiplexed symbolsequences X1–XM.[X1 X2 . . . XM] ^(T) =[S1 S2 . . . SK]·V  (10)

The vector-multiplexed symbol sequences X1–XM are constituted withvector-multiplexed transmission frames 800-1–800-M in the number of M asshown in FIG. 8. Those are to be transmitted correspondingly to theantenna elements A1–AM structuring the base station array antenna 105.

The base station RF section 302 converts the vector-multiplexed symbolsequences X1–XM respectively into radio-frequency-band signals. Theconverted signals are transmitted to the communicating terminal 102through the antenna elements A1–AM structuring the base station arrayantenna 105.

Now explanation is made below on the receive operation at thecommunicating terminal 102 using FIG. 4.

At first, in the terminal transmitter-receiver section 107 of thecommunicating terminal 102, the terminal RF section 402 converts thereceived signal at the terminal antenna 106 into a received symbolsequence Y0, or baseband signal, and outputs it to the decode means 403.The decode means 403, received a transmission frame 700-1, uses as aninput the received symbol sequence Y0 and executes framesynchronization, information source authentication, demodulation of thedata sequence D1 based on modulation scheme and frame error checkprocess, thereby restoring the data sequence D1 and outputting it as areceived data sequence.

Here, provided that the received symbol sequence as a received signal atthe non-communicating terminal 200 is Y1 and the propagation channelmatrix as a featuring of between the base station 101 and thenon-communicating terminal 200 is Hl, the received symbol sequences Y0and Y1 as received signals at the communicating terminal 102 arerespectively expressed by equations as in the following:Y0=H·X+N0  (11)Y1=H1·X+N1  (12)

Here, X is a vector denotation of the vector-multiplexed symbolsequences X1–XM and denoted by use of (Equation 10) as in the following.

$\begin{matrix}\begin{matrix}{X = {\left\lbrack {{S1}\mspace{14mu}{S2}\mspace{11mu}\ldots\mspace{20mu}{SK}} \right\rbrack \cdot V}} \\{= \left\lbrack {{{S1} \cdot {v1}}\mspace{14mu}{{S2} \cdot {v2\ldots}}\mspace{14mu}{{SK} \cdot {vK}}} \right\rbrack}\end{matrix} & (13)\end{matrix}$

Meanwhile, N0 and N1 respectively represent noised components containedin the received symbol sequences Y0 and Y1. Accordingly, Y0 can bechanged to the following equation, from (Equation 11) and (Equation 13).Y0=H·(v1·s1+v2·S2+. . . +vK·SK]+N0  (14)

Meanwhile, the propagation channel matrix H, because to be decomposed bysingular values and orthogonal matrixes as in (Equation 4), is expressedaccording to the characteristic shown in (Equation 5), (6) and (7), asin the following.H·vk=δ, k=1=0, k≠1  (15)

Furthermore, if considering in (Equation 14) the condition of (Equation15), Y0 is expressed as in the following.Y0=δ·S1+N0  (16)

Here, provided that the mean power of a noise component N0 is Pn0 andreceived SINR at the communicating terminal 102 is SINR0, SINR0 can beexpressed by the following equation.SINR0=(δ·S1)² /Pn0  (17)

This shows that SINR0 can be set at a proper value by control oftransmit power to S1, i.e. norm of v1.

Likewise, using (Equation 12) and (Equation 13), Y1 is given by thefollowing equation.Y1=H1·(v1·S1+v2·S2+. . . +vK·SK)+N1  (18)

Meanwhile, when the product of the propagation channel matrix H1 and thevectors v1–vK is given γ k, the following relationship is held.H1·vK=γk  (19)

Furthermore, from (Equation 18) and (Equation 19), Y1 is expressed bythe following equation.Y1=γ1·S1+γ2·S2+. . . γK·SK+N1  (20)

Here, it is assumed that the mean power of noise component N1 is givenPn1 and the received signal power of symbol sequence S1 is a desiredsignal component at the non-communicating terminal 200.

In this case, provided that the received SINR at the non-communicatingterminal 200 is SINR1, SINR1 is expressed by the following equation.SINR1=(γ1·S1)²/{(γ2·S2)²+. . . (γK·SK)² +Pn1}  (21)

It is generally known that, in mobile communication environment, whereterminal-to-terminal distance is as far as a carrier frequencywavelength, propagation channel is approximated to non-correlation.Particularly, in the system of cellular telephony, wireless LAN or thelike utilizing a microwave band wherein carrier frequency wavelength isas small as dozens of centimeters or smaller, the propagation channelsobserved between terminals can be approximated as non-correlated. Forexample, assuming such a propagation environment of mobilecommunication, the vectors v2–vK orthogonal to the propagation channelmatrix H in this embodiment could have correlations to the propagationchannel matrix H1. Namely, because γ2–γK become not zero, the followingis held from a statistic viewpoint.SINR0>SINR1Accordingly, because of (transmission error rate at the communicatingterminal 102)<(transmission error rate at the non-communicating terminal200), there is a reduced probability for the non-communicating terminal200 to demodulate the symbol sequence S1 freely from errors and restorethe data sequence D1, as compared to the communicating terminal 102.

The explanation made so far was on the case that the vector controlmeans 304 calculated a vector space V or V′ obtainable by singular-valueor eigen-value decomposition of the propagation channel matrix H havingM rows and M columns. This however is a mere one example for obtainingsuch v2–vM as having low correlation to the column vector v1constituting a vector space V. Namely, the vector control means 304satisfactorily calculates such a vector space V that column vectorsv2–vM are linearly independent of the column vector v1 rather than thepropagation channel matrix H or such a vector space that column vectorsv2–vM are orthogonal to the column vector v1. Thus, there is nolimitation in the method of calculating the same.

Explanation is now made on the case of using BPSK as a modulation schemeon the data sequences D1–DK, as an analysis example of demodulationcharacteristic in the communicating terminal 102 and non-communicatingterminal 200, by use of FIG. 9.

FIGS. 9 a to (c) show a simulation analysis result in the presence ofthe base station 100, and communicating terminal 102 and thenon-communicating terminal 200.

FIG. 9 a is a signal waveform of a data sequence D1 produced at the basestation 101, FIG. 9 b is a signal waveform of a received data sequenceobtained as a result of demodulation at the communicating terminal 102,and FIG. 9 c is a signal waveform of a received data sequence obtainedas a result of demodulation at the non-communicating terminal 200. Thesimulation is under the condition that the number of antenna elements Mconstituting the base station array antenna 105 is 8, the data sequenceD1 has data in the number of 100, and the data sequences to betransmitted with vector multiplexing from the base station 101 are inthe number of 8equal to the number of antennas. Meanwhile, the elementsh1–h8 of a propagation channel matrix H are produced by use of (Equation22), according to the Rayleigh probability distribution.hm=N(0, ½)+j*N(0, ½), m=1 . . . , 8  (22)Note that N(0, ½) is a function to produce random numbers according to anormal probability distribution having a mean of 0 and a standarddeviation of ½.

As noted before, at the base station 101, the vector multiplexing means301 transmits, with vector multiplexing, the symbol sequences S1–S8 fordata sequences D1–D8 by use of vectors v1–v8. The vectors v1–v8 arecalculated from a propagation channel matrix H describing of acharacteristic of the propagation channel 103 of between the basestation 101 and the communicating terminal 102, having a featureorthogonal one to another wherein the vector v1 only has a highcorrelation to the propagation channel matrix H. Accordingly, as shownin FIG. 9 b, the data sequence D1, vectorized based on the vector v1, isto be demodulated correctly at the communicating terminal 102.

Meanwhile, the propagation channel 201, of between the non-communicatingterminal 200 and the base station 101, has a correlation also to thevectors v2–v8, allowing for reception of symbol sequences S2–SKsimultaneously with the symbol sequence S1 for the data sequence D1.Accordingly, because of a difficulty in detecting and correctlyrestoring the data sequence D1 at the non-communicating terminal 200 asshown in FIG. 9 c, the data sequence D1 for transmission to thecommunicating terminal 102 can be prevented from leaking to thenon-communicating terminal 200.

Using FIG. 10, explanation is now made on the result of a simulation ofstatistic evaluation as to the leak ratio of the data sequence D1 to thenon-communicating terminal 200. The propagation channel matrix H isproduced by use of (Equation 22) based on the Rayleigh probabilitydistribution, similarly to the case of FIG. 9. FIG. 10 shows the numberof antenna elements M of the base station array antenna 105 on theabscissa and a leak ratio of data on the ordinate. The leak ratio Z hereis agreed according to (Equation 23) by using the number of times L thatdata leak is to be considered when the propagation channel matrix H topropagation channel 201 is updated N times. Assumption is made herethat, at the non-communicating terminal 200, there is considered a dataleak in the case that the data sequence D1 having data in the number of128 has been demodulated without encountering errors.Z=(L/N)×100 [%]  (23)

However, the leak ratio as agreed by (Equation 23) is assumablycalculated under the condition that, at the base station 101, the numberof data sequences K to be transmitted with vector multiplexing is equalto the number of antenna elements M, i.e. K=M.

As shown in FIG. 10, the leak ratio Z of data decreases with increase inthe number of antenna elements M. At M=8, i.e. when the base stationarray antenna 105 has the number of antenna elements of 8, the data leakratio is secured at 0.1%. Namely, by employing the arrangement of radiocommunication system 100 of this embodiment, the concealment ofcommunication data can be enhanced without carrying out the encryptionprocess to the communication data.

Meanwhile, where the radio communication system 100 is utilized on amobile communication system such as of cellular telephony or WLAN, thepropagation channel 103 has a characteristic fluctuates in time withmovement of the communicating terminal. In case the communication datato the communicating terminal 102 should be received for a given time ina location where a non-communicating terminal 200 exists, there is anextreme difficulty in continuously receiving the communication data.

Incidentally, at the base station 101, the encode means 600-1–600-Kexecuted the symbol-mapping process on the data sequences D1–DK by useof the same modulation scheme. Alternatively, symbol-mapping process maybe executed on the data sequences D1–DK by using different modulationschemes, to produce a plurality of symbol sequences S1–SK different insymbol information. Besides, by making the encode means 600-1–600-Kexecute a code spreading process on the data sequences D1–DK with use ofdifferent code sequences, a plurality of symbol sequences S1–SK may beproduced that are different in symbol information.

In this manner, in the case of producing symbol sequences S1–SK by usingdifferent modulation schemes or spread codes, demodulation process isenabled at the communicating terminal 102 by estimating a modulationscheme or spread codes from a received symbol sequence Y0 by means ofthe demodulating means 403 at the communicating terminal 102 orpreviously sharing the modulation scheme or spread codes. Meanwhile, byallowing the demodulating means 403 to estimate a modulation scheme or aspread code, the base station 101 may change the modulation scheme orspread codes with passage of time. This can reduce the data leak ratioto the non-communicating terminal 200 without increasing the number ofantenna elements M of the base station array antenna 105.

Incidentally, the process that the base station 101 received the datasequence D0 sent from the communicating terminal 102 is as per thefollowing.

Namely, the array-combined receiving means 305 uses, as an input, thereceived symbol sequences Y1–YM and the vector space V′ calculated inthe vector control means 304, and makes a weight-combining process ofthe vector space V′ on the received symbol sequences Y1–YM by use of(Equation 24), thus obtaining vector-combined signals C1–CL. Here, it isassumed that the foregoing column vectors Vs or Ve are selected and usedfor the vector space V′.[C1 C2 . . . CL]=[Y1 Y2 . . . YM]·V′  (24)

The vector-combined signal C1 obtained by (Equation 24) is a receivedsignal obtained by combining the reference signal x0 sent from thecommunicating terminal 102 with a directivity of the base station arrayantenna 105. Meanwhile, there is a possibility that the vector-combinedsignals C2–CM contain an interference signal component of from thenon-communicating terminal 200. Thus, it is possible to estimate adesired-signal-power to interference-signal-power ratio from the signalpower of the vector-combined signal C1 and the vector-combined signalsC2–CM. Furthermore, the array-combined receiving means 305 executesframe synchronization, terminal authentication, demodulation of the datasequence D0 based on modulation scheme and frame error check process,thus restoring the data sequence D0 and outputting it as a received datasequence.

Meanwhile, a receiving process using an MMSE (Minimum Mean Square Error)method [1] is possible to carry out in place of using, as a vector spaceV′ for use upon receiving, Vs or Ve obtained by singular-valuedecomposition or eigen-value decomposition of H as in the foregoing.

[1] B. Widrow, P. E. Mantey, L. J. Griffiths, and B. B. Goode, “AdaptiveAntenna Systems”, Proc. IEEE, vol. 55, no. 12, pp. 2143–2158, December1967.

In this case, the propagation channel analyzing means 303 uses, as aninput, the received symbol sequences Y1–YM and produces a correlationvector r of between complex conjugate value R0′ to reference symbol R0,or reference signal, and Y1–Ym according to (Equation 25). A correlationmatrix R to propagation channel matrix H is determined by (Equation 8)and outputted to the vector control means 304.r=[Y1Y2 . . . YM] ^(T) ×R0′  (25)

Thereupon, the vector control means 304 uses the correlation vector rand correlation matrix R, and calculates a vector v1 by use of (Equation26). The value is to be updated by using the steepest descent method,etc.vr=R ⁻¹ ·r  (26)

Note that R⁻¹ represents an inverse matrix to R. In this case, thearray-combined receiving means 305 uses, as an input, the receivedsymbol sequences Y1–YM and the vector vr, and produces a vector-combinedsignal C1 by a weight-combining process of vr to the Y1–YM through useof (Equation 27).C1=[Y1Y2 . . . YM]·vr  (27)

Then, for the vector-combined signal C1, executed are framesynchronization, terminal authentication, demodulation of the datasequence D0 based on modulation scheme and frame error check process,thereby restoring the data sequence D0 and outputting it as a receiveddata sequence.

Using FIG. 11, explanation is made on the flow of from an establishmentof radio-circuit synchronization to a completion of data transmission,in a radio communication system 100 having the base station 101 andcommunicating terminal 102 arranged as above for operation, from aviewpoint of communication procedure.

Process 0: Initialization of the Base Station 101 and CommunicatingTerminal 102

The base station 101 and the communicating terminal 102 are both set inan initial state immediately after turning on the power or by receivinga particular signal. Simultaneously, the states of frequency, time,synchronization, etc. are established according to a procedure agreedbeforehand (step

After a given time from the completion of these initial operations, thebase station 101 puts control information on a control signal andtransmits it at a constant time interval (step S1102).

Meanwhile, the communicating terminal 102, after completing the initialoperation (step S1101), begins to search for a control signal. When thecommunicating terminal receives the control signal sent from the basestation, the communicating terminal 102 detects its time, frequency,etc. and synchronizes those with the time and frequency held on thesystem (hereinafter, this is referred to as “system synchronization)(step S1102). After system synchronization is normally completed, thecommunicating terminal 102 transmits a registration request signal tothe base station in order to notify the presence thereof (step S1103).The base station 101 transmits a registration allowance signalresponsive to the registration request from the communicating terminal102, thereby giving registration allowance to the terminal (step S1104).

Process 1: Reference Symbol Transmission by the Communicating Terminal102

The communicating terminal 102 outputs a reference signal X0 containinga reference symbol R0 for the base station 101 to analyze thepropagation channel 103 (step S1105). Specifically, the reference-symbolproducing means 400 of the communicating 102 produces a previouslyagreed particular reference symbol R0 and makes up a transmission frameF0, thus outputting it as a symbol sequence S0. The terminal RF section402 converts the symbol sequence S0 into a radio-frequency-band signaland transmits it as a reference signal x0 through the terminal antenna106 (step S1105).

The base station 101 waits for a reference signal x0 received at thebase station array antenna 105 through the propagation channel 103 fromthe communicating terminal 102 (step S1105). The received signals at theantenna elements A1–AM, in the base station RF section 302, arerespectively converted into received symbol sequences Y1–YM, or basebandsignals. The propagation channel analyzing means 303 uses the receivedsymbol sequences Y1–YM as an input and produces a propagation channelmatrix H as a parameter featuring the propagation channel 103. Then, thevector control means 304 calculates a vector space V as to H andproduces column vectors v1–vK constituting the vector space V.

Process 2: Vectorized Signal Transmission by the Base Station 101

The base station 101 transmits vectorized signal x1–xK to thecommunicating terminal 102 by use of the base station array antenna 105(step S1106). Specifically, taking the data sequences D1–DK as an input,the multi-symbol producing means 300 executes a symbol-mapping processover a complex plane according to modulation scheme, and makes uptransmission frames 700-1–700-K, thus outputting those as symbolsequences S1–SK. The vector multiplexing means 301 uses the symbolsequences S1–SK as an input, and executes a vector multiplex processusing vectors v1–vK and produces vector-multiplexed symbol sequencesX1–XM. The vector-multiplexed symbol sequences X1–XM are sent withcorrespondence thereof to the antenna elements A1–AM structuring thebase station array antenna 105. The base station RF section 302 convertsthe vector-multiplexed symbol sequences X1–XM respectively intoradio-frequency-band signals and transmits those as vectorized signalsx1–xK through the base station array antenna 105.

From then on, vector-multiplexed communication of process 2 and usualcommunication are repeatedly done.

Explanation was made so far on process 0 as the initializationoperation. This however is assumed on the general operation, and henceis not a requisite proceeding for the invention.

Meanwhile, in process 1, the propagation channel was analyzed by sendingthe reference signal. This is because the propagation parametergenerally can be estimated higher in accuracy rather by use of a knownsignal, i.e. propagation channel analysis can be done even unless usingespecially a reference signal. In other words, propagation parameterscan be estimated by utilization, for example, of a control signal as inprocess 0, a registration request signal, a registration permissionsignal or the like.

Incidentally, because the invention is characterized in that a pluralityof data sequences are transmitted with vector multiplexing throughutilization of the characteristic of the propagation channel 103 ofbetween the particular communicating terminal 102 and the base station101, there are possible cases to raise a problem where there aremovement occurrences of the base station or the communicating terminal.However, in this case, the problem can be avoided by repeatedlytransmitting and receiving the reference signal after movement, as insteps S1107 and S1108 shown in FIG. 11.

As described above, in the radio communication method of the invention,by controlling a propagation channel SINR decisive for the error ratioof a radio transmission channel, third party's received SINR is degradedwhile securing a certain level or more of received SINR at betweenparticular radio stations for mutual data transmissions simultaneously.By raising the error occurrence probability of the signal sequence forthe third party to demodulate, the data requiring concealment can beprevented from leaking to the third party through a radio communicationchannel.

Meanwhile, in the transmitter apparatus of the invention, although thepropagation channel matrix H if deteriorated in estimation accuracycauses a deterioration of SINR to the communicating terminal but doesnot change the probabilistic distribution characteristic of SINR to thenon-communicating terminal. Namely, where assured is the condition thatthe SINR to the communicating terminal 102 is at or higher thanreceiving sensitivity, there is no increase of data leak ratio.Accordingly, as compared to the point that the prior art concerningencryption key generation based on propagation parameters reliesdirectly upon the estimation accuracy of propagation parameter, thetransmitter apparatus of the invention can prevent against data leak onthe communication physical layer in a state securing the robustness ofdata transmission, in the radio-wave propagation environment beingcomplex and always varying in time as in a mobile communicationenvironment, thus resultingly providing high level of security.

Furthermore, those processes can be implemented independently of theencryption and decryption using the conventional arithmetic technique.Therefore, higher level of security is to be expected by implementingthe invention in addition to the prior art.

(Embodiment 2)

The present embodiment is explained with using FIGS. 1 and 12 to 16.

The system overall arrangement in the present embodiment is as per theradio communication system 100 shown in FIG. 1, similarly toembodiment 1. FIG. 12 is a block diagram showing a configuration of abase station 101. This is different from embodiment 1 in that having areference-symbol producing means 1200 and propagation channelinformation receiving means 1201. The reference-symbol producing means1200 includes a reference signal previously shared between the basestation 101 and the communicating terminal 102, to produce a referencesymbol for calculating a propagation parameter. The propagation channelinformation receiving means 1201 is to take, as an input, a receivedsymbol sequences from a base station RF section 302 and execute framesynchronization, information-source authentication, demodulation ofpropagation channel information symbol sequence and frame error checkprocess, thus producing a propagation channel matrix.

FIG. 13 is a block diagram showing a configuration of the communicatingterminal 102. This is different from embodiment 1 in that havingpropagation channel analyzing means 1300 and encode means 1301. Thepropagation channel analyzing means 1300 is to produce a propagationchannel matrix H as a propagation parameter by use of received symbols.The encode means 1301 is to execute a symbol-mapping process requiredfor radio transmission on the propagation channel matrix data, andproduce propagation channel information symbol sequences.

The radio communication system 100 configured as above is explained indetail below mainly on the points different from embodiment 1, withusing FIGS. 1, 12 and 13.

At first, transmit signals x′1–x′M containing a reference symbol aresent from the base station 101 through the antenna elements A1–AM of thebase station array antenna 105. The transmit signals x′1–x′M containinga reference symbol are to be received by the communicating terminal 102in order to analyze the propagation channel 103, which includes areference signal previously shared between the base station 101 and thecommunicating terminal 102.

In FIG. 12, the reference-symbol producing means 1200 producesparticular reference symbols R1–RM previously agreed between the basestation and the communicating terminal 102 and outputs those to thevector multiplexing means 301. The vector multiplexing means 301produces a vector-multiplexed symbol sequences X′1–X′M that thereference symbols R1–RM are inserted in vector-multiplexed symbolsequences X1–XM which the symbol sequences S1–SK are vector-multiplexedby use of a vector space V. Here, the reference symbols R1–RM areassumably produced from code sequences orthogonal one to another ordifferent in a manner lowering correlation. Incidentally, FIG. 14 showsa structural example of transmission frames 1400-1–1400-M that thevector multiplexing means 301 inserted mutually-different referencesymbols R1–RM to the vector-multiplexed symbol sequences X1–XM.

Here, because the data sequences D1–DK are inserted as required, theframe structure may be to send only the reference symbols R1–RM wherethe vector-multiplexed symbol sequences are used merely for the purposeof analyzing the propagation channel 103.

Meanwhile, FIG. 15 shows a structural example of transmission frames1500-1–1500-M that the vector multiplexing means 301 inserted only thereference symbol R1 to the vector-multiplexed symbol sequences X1–XM.The transmission frames 1400-1–1400-M use the reference symbols R1–RMproduced from the code sequences different one from another whereas theframe structure shown in FIG. 15 has reference symbols R1 inserted inthe respective frames in their positions shifted in time wherein thereis no need to produce reference symbols R1–RM by use of code sequencesin the number equal to the number of antenna elements M.

The vector-multiplexed symbol sequences X′1–X′M, made up by thetransmission frames 1400-1–1400-M or 1500-1–1500-M produced by thevector multiplexing means 301, are converted in their symbol sequencesS1–SM into radio-frequency-band signals, in the base station RF section302. Those are transmitted as transmit signals x′1–x′M containingreference symbols R1–RM by being put in correspondence to the arrayantenna elements A1–AM structuring the base station array antenna 105.

Then, at the communicating terminal 102, the propagation channel 103 isanalyzed on the basis of the received signals containing the referencesymbols. Thereafter, the communicating terminal 102 sends a result ofthe same to the base station 101. Explanation is made below on theprocedure for feeding the analysis result back to the base station 101.

The transmit signals x′1–x′M, sent from the base station array antenna105, are propagated through the propagation channel 103 and combinedlyreceived at a of receiving point of the terminal antenna 106. Theterminal RF section 402 converts the reception signal into a receptionsymbol sequence Y′0, or baseband signal. By use of the received symbolY′0, the propagation channel analyzing means 1300 produces a propagationchannel matrix H shown in (Equation 1), as a propagation parameterfeaturing the propagation channel 103. Specifically, where thetransmission frames produced by the vector multiplexing means 301 of thebase station 101 are structured by mutually-different reference symbolsin the number of M as in 1400-1 to 1400-M, the propagation channelanalyzing means 1300 of the communicating terminal 102 executes acorrelation operation process of multiplying R1–RM separately on thereceived signal Y′0 by use of the previously-known reference symbolsR1–RM, and determines H1–HM as elements of a propagation channel matrixH from the amplitude and phase information of the signal obtainedtherefrom. This places the propagation channel coefficients of betweenthe antenna elements A1–AM of the base station array antenna 105 and theterminal antenna 106, in correspondence respectively to H1–HM.

Meanwhile, in the case the transmission frame produced in the vectormultiplexing means 301 of the base station 101 is structured arrangedwith reference symbols in positions shifted in time as in 1500-1–1500-Mshown in FIG. 5, the propagation channel analyzing means of thecommunicating terminal 102 also determines amplitude and phaseinformation of a received symbol Y′0 while shifting the timing ofsampling, by use of a previously-known reference symbol. This makes itpossible to calculate the elements h1–hM constituting the propagationchannel matrix H.

The encode means 1301 takes, as an input, the propagation channel matrixH data produced by the propagation channel analyzing means 1300 andexecutes a symbol-mapping process required for radio transmissionthereby producing a propagation channel information symbol sequence C0.The symbol producing means 401 produces a transmission frame 1600inserted with a propagation channel information symbol sequence C0 asshown in FIG. 16, and outputs it as a symbol sequence S′0. The terminalRF section 402 converts the symbol sequence S′0 into aradio-frequency-band signal and transmits it as a transmit signal x′0 atthe terminal antenna 106.

Then, the base station 101 receives the transmit signal x′0 containingpropagation channel information at the base station array antenna 105.The received signal, in the base station RF section 302, is convertedinto received symbol sequences Y′1–Y′M, or baseband signal. Thepropagation channel information receiving means 1201 takes, as an input,part or all of the received symbol sequences Y′1–Y′M and executesthereon frame synchronization, information-source authentication,demodulation of the propagation channel information symbol sequence C0and frame error check process, thus outputting a propagation channelmatrix H. With the use of the propagation channel matrix H generated bythe propagation channel information receiving means 1201, the vectorcontrol means 304 produces a transmit vector space V and receivingvector space V′ for the base station 101 to make a transmitting to andreceiving from the communicating terminal 102.

According to the arrangement as in the above, by feeding a determinedpropagation channel matrix H back to the base station 101 by thepropagation channel analyzing means 1300 in the communicating terminal102, the base station 101 is allowed to correctly obtain propagationchannel information to the terminal antenna 106 as viewed from the basestation array antenna 105. Therefore, because the base station 101 is tocalculate a vector space by using a propagation channel matrix H for thedownlink as viewed from the base station 101 and carries out avector-multiplexed transmission, system performance can be maintainedeven under such a condition that there is an unignorable asymmetry as tothe downlink and uplink.

Meanwhile, although the communicating terminal 102 is configured to feedthe propagation channel matrix H back to the base station 101, thefeedback information may be by notifying another propagation parameter,vector space, etc. to be estimated from the propagation channel matrixH. In this case, the communicating terminal 102 has a function for theFIG. 13 propagation channel analyzing means 1300 to estimate apropagation parameter or vector space by use of a propagation channelspace H and feed the result thereof to the base station 101.

Using FIG. 17, explanation is made on the flow of from establishingradio-circuit synchronization to a completion of data transmission in aradio communication system 100 having the base station 101 andcommunicating terminal 102 arranged for operation as above, from aviewpoint of communication procedure.

Process 10: Initialization of the Base Station 101 and CommunicatingTerminal 102

The initialization operation is same as embodiment 1.

Process 11: Transmission of Reference Symbols from the Base Station 101

The base station 101 outputs transmit signals X′1–X′M containingreference symbols R1–RM for the communicating terminal 102 to analyzethe propagation channel 103 (step S1701). Specifically, thereference-symbol producing means 1200 produces reference symbols R1–RM,while the vector multiplexing means 301 makes up transmission framesinserted with the reference symbols R1–RM and outputs vector-multiplexedsymbol sequences X′1–X′M. The vector-multiplexed symbol sequencesX′1–X′M, in the base station RF section 302, are converted intoradio-frequency-band signals so that transmit signals x′1–x′M containingreference symbols R1–RM are transmitted correspondingly to the antennaelements A1–AM structuring the base station array antenna 105.

Process 12: Transmission of Propagation Channel Information from theCommunicating Terminal

The communicating terminal 102 waits for the transmit signals X′1–X′Mtransmitted at the antenna elements A1–AM of the base station 101 andreceived at the terminal antenna 106 through the propagation channel103. In the case of receiving at the terminal antenna 106 of thecommunicating terminal 102, the received signals at the terminal RFsection 402 are converted into a received symbol sequence Y′0, orbaseband signal. The propagation channel analyzing means 1300 takes thereceived symbol sequence Y′0 as an input and produces a propagationchannel matrix H as a propagation parameter featuring the propagationchannel 103 depending upon the amplitude and phase information of thereference symbols R1–RM, in accordance with the transmission framestructure.

Then, the propagation channel matrix H data, in the encode means 1301,is subjected to a symbol-mapping process for radio transmission andthen, in the symbol producing means 401, inserted as a part of the datasequence structuring the transmission frame, thus producing a symbolsequence X′0. The symbol sequence X′0 is outputted to the terminal RFsection 402 where it is converted into a radio-frequency-band signal,thus being transmitted as a transmit signal x′0 at the terminal antenna106 to the base station 101 (step S1702).

Process 13: Transmission of a Vectorized Signal from the Base Station101

At the base station 101, the propagation channel information receivingmeans 1201 demodulates the received signal of x′0 sent from thecommunicating terminal 102 and produces a propagation channel matrix Has a propagation parameter featuring the propagation channel 103. Then,the vector control means 304 calculates a vector space V as to thepropagation channel matrix H and produces column vectors v1–vkconfiguring the vector space V.

Thereafter, in the base station 101, when there is an occurrence of datasequences D1–DK to be transmitted to the communicating terminal 102, themulti-symbol producing means 300 executes a symbol-mapping process ofthe data sequences D1–DK over the complex plane according to modulationscheme and makes up transmission frames 700-1–700-K, thus outputtingsymbol sequences S1–SK to the vector multiplexing means 301. The vectormultiplexing means 301 takes the symbol sequences S1–SK as an input andexecutes a vector-multiplexing process thereon with use of columnvectors v1–vK, to produce vector-multiplexed symbol sequences X1–XM. Thevector-multiplexed symbol sequences X1–XM are sent with correspondencethereof to the antenna elements A1–AM structuring the base station arrayantenna 105. Incidentally, the base station RF section 302 converts thevector-multiplexed symbol sequences X1–XM respectively intoradio-frequency-band signals and transmits those as vectorized signalsx1–xK through the base station array antenna 105 (step S1703).

Thereafter, the base station 101 and the communicating terminal 102repeat the vector-multiplexed communication of process 13 and the usualcommunication.

In the above explanation, process 10 as the initialization process isassumed on the general operation and hence is not requisite procedurefor the invention.

Meanwhile, in process 11, the propagation channel was analyzed bytransmitting reference signals. This is because the use of a knownsignal generally allows for estimating a propagation parameter withhigher accuracy. Propagation channel analysis is available even wherenot using especially a reference signal. In other words, the propagationparameter can be estimated by utilization of a control signal, e.g., inprocess 10, a registration request signal, a registration permissionsignal or the like.

Incidentally, there is a case to raise a problem upon an occurrence ofbase station or communicating-terminal movement, because the inventionis characterized to transmit a plurality of data sequences with vectormultiplexing by utilization of the characteristic of a propagationchannel 103 of between the particular communicating terminal 102 and thebase station 101 similarly to embodiment 1. However, in this case, theproblem can be avoided by repeatedly transmitting and receiving thereference signals as in steps S1704 and S1705 shown in FIG. 17.

In the transmitter apparatus of the invention so far explained, althoughthe estimation accuracy of the propagation channel matrix H ifdeteriorates causes SINR deterioration to the communicating terminal102, there is no change in the probabilistic distribution characteristicof SINR to the non-communicating terminal 200. Namely, where thecondition is assured that the SINR to the communicating terminal 102 isat or higher than receiving sensitivity, there is no increase of dataleak ratio.

Accordingly, as compared to the point that the prior art concerningencryption key generation based on propagation parameters reliesdirectly upon the estimation accuracy of propagation parameter, thetransmitter apparatus of the invention can prevent against data leak onthe communication physical layer in a state securing the robustness ofdata transmission, in the radio-wave propagation environment beingcomplex and always varying in time as in a mobile communicationenvironment, thus resultingly providing high level of security.

Furthermore, those processes can be implemented independently of theencryption and decryption using the conventional arithmetic technique.Therefore, higher level of security is to be expected by implementingthe invention in addition to the prior art.

Industrial Applicability

The present invention is useful for a transmitter for transmittinginformation between particular radio stations, and suited for preventinginformation from leaking to a third party on the radio communicationchannel.

1. A transmitter apparatus for transmitting an information symbolsequence from a first radio station having an array antenna having M (Mis a positive integer and M>1) elements to a second radio station, thetransmitter apparatus comprising: vector control means for producing aplurality of N (N is a positive integer) dimensional vectors, where N≦M;and vector multiplexing means for producing an M number ofvector-multiplexed symbol sequences multiplexed by multiplying theplurality of N dimensional vectors by a plurality of symbol sequencescontaining the information symbol sequence and for transmitting thevector-multiplexed symbol sequences through the array antenna; whereinthe vector control means produces the plurality of N dimensional vectorsbased on a propagation parameter corresponding to a propagation channelbetween the first radio station and the second radio station independentof other propagation channels, and the vector control means produces theplurality of N dimensional vectors such that, at the second radiostation, at least one symbol sequence containing the information symbolsequence is received from among the plurality of symbol sequences andother symbol sequences are canceled.
 2. A transmitter apparatusaccording to claim 1, further comprising propagation channel analyzingmeans for producing a propagation channel matrix as the propagationparameter, wherein said vector control means produces the plurality of Ndimensional vectors based on singular-value decomposition of thepropagation channel matrix.
 3. A transmitter apparatus according toclaim 1, further comprising propagation channel analyzing means forproducing a propagation channel matrix as the propagation parameter,wherein said vector control means produces the plurality of Ndimensional vectors based on eigen-value decomposition of a correlationmatrix of the propagation channel matrix.
 4. A transmitter apparatusaccording to claim 1, further comprising reference symbol producingmeans for producing a reference symbol known to the second radiostation; and propagation channel information receiving means forreceiving information associated with the propagation parametertransmitted from the second radio station and for determining thepropagation parameter from the received information, wherein theinformation associated with the propagation parameter is produced fromthe propagation parameters, the propagation parameter being determinedby the second radio station from the reference symbol transmitted fromthe first radio station.
 5. A transmitter apparatus according to claim1, wherein the plurality of symbol sequences are, in part or all,symbol-mapped based on modulation schemes different from each other. 6.A transmitter apparatus according to claim 1, wherein the plurality ofsymbol sequences are, in part or all, spread by code sequences differentone from each other.
 7. A radio communication method for transmitting aninformation symbol sequence from a first radio station having an arrayantenna having M elements to a second radio station, where M is apositive integer and M>1, the radio communication method comprising thesteps of: producing a plurality of N dimensional vectors by the firstradio station, where N is a positive integer and N≦M, such that, at thesecond radio station, at least one symbol sequence containing theinformation symbol sequence is received from among a plurality of symbolsequences containing the information symbol sequence and other symbolsequences are canceled; multiplying the plurality of N dimensionalvectors by the plurality of symbol sequences containing the informationsymbol sequence and producing an M number of vector-multiplexed symbolsequences; and transmitting the vector-multiplexed symbol sequences fromthe first radio station to the second radio station through the arrayantenna wherein the step of producing the plurality of N dimensionalvectors produces the plurality of N dimensional vectors based on apropagation parameter corresponding to a propagation channel between thefirst radio station and the second radio station independent of otherpropagation channels.
 8. A radio communication method according to claim7, including the step of transmitting a reference signal from the secondradio station to the first radio station, the reference signal includinga reference symbol known to the first radio station, wherein, the firstradio station calculates the propagation parameter based on thereference symbols.
 9. A radio communication method for transmitting aninformation symbol sequence from a first radio station having an arrayantenna having M elements to a second radio station, where M is apositive integer and M>1, the radio communication method comprising thesteps of: a reference signal from the first radio station to the secondradio station, the reference signal containing reference symbols knownto the second radio station; producing a channel information symbolsequence by the second radio station from the received reference signal,the channel information symbol sequence containing a propagationparameter corresponding to a propagation channel between the secondradio station and the first radio station independent of otherpropagation channels; transmitting the channel information symbolsequence from the second radio station to the first radio station;producing a plurality of N (N is a positive integer) dimensional vectorsby the first radio station, where N≦M, such that, at the second radiostation, at least one symbol sequence containing the information symbolsequence is received from among a plurality of symbol sequencescontaining the information symbol sequence and other symbol sequencesare cancelled based on the propagation parameter extracted from channelinformation symbol sequences received by the first radio station;multiplying the plurality of N dimensional vectors by the plurality ofsymbol sequences containing the information symbol sequence andproducing an M number of vector-multiplexed symbol sequences; andtransmitting the vector-multiplexed symbol sequences from the firstradio station to the second radio station through the array antenna.